VERTEBRAL DEFORMITY IN PATIENTS with osteoporosis

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1 ORIGINAL ARTICLE Effects of Reducing Resistance, Repetitions, and Frequency of Back-Strengthening Exercise in Healthy Young Women: A Pilot Study Michio Hongo, MD, Eiji Itoi, MD, Mehrsheed Sinaki, MD, Yoichi Shimada, MD, Naohisa Miyakoshi, MD, Kyoji Okada, MD ABSTRACT. Hongo M, Itoi E, Sinaki M, Shimada Y, Miyakoshi N, Okada K. Effects of reducing resistance, repetitions, and frequency of back-strengthening exercise in healthy young women: a pilot study. Arch Phys Med Rehabil 2005;86: Objective: To determine the effects of reducing intensity or frequency of back-strengthening exercise on back extensor strength. Design: Randomized controlled trial. Setting: Exercises were performed in participants homes. Instruction and measurements were performed at the rehabilitation center in the hospital. Participants: Fifty-eight healthy female volunteers (mean age, 20y). Interventions: Participants were assigned to 1 of 5 exercise intervention groups: control; standard protocol (STD) that has been shown to increase back extensor strength; weight reduction (WRD); repetition reduction (RRD); and frequency reduction (FRD). Back exercises involved lifting a weighted backpack while in a prone position. The study period was 12 weeks. Main Outcome Measure: Isometric back extensor strength. Results: Back extensor strength increased significantly in all groups except the control group. The maximum increase was achieved by the STD group (39%), followed by the FRD (25%), WRD (22%), RRD (20%), and control (5%) groups. Percentage change in back extensor strength was significantly greater in the STD group than in all other groups except the FRD group. Conclusions: Back extensor strength in the WRD, RRD, and FRD groups was significantly higher at 12 weeks compared with baseline. Reductions in intensity and frequency resulted in similar effects on increases in back extensor strength. Key Words: Back; Exercise; Muscles; Rehabilitation; Women by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation VERTEBRAL DEFORMITY IN PATIENTS with osteoporosis can cause substantial pain, disability, loss of height, and increased risk of new vertebral fractures. 1-3 Associations have been noted between kyphosis, vertebral compression fractures, and decreased back extensor muscle strength. 4-7 Back extensor strength has a significant negative correlation with thoracic kyphosis and physical activity. 8 Increasing the strength of the back extensors may thus help to reduce or prevent kyphosis associated with osteoporosis. We have reported that back muscle exercises using a specific backpack are effective in increasing back extensor strength 9,10 and decreasing risk of vertebral fractures. 11 Subjects in these studies were healthy postmenopausal women. The same intensity of exercise, when performed by patients with osteoporosis, may cause back pain or even vertebral fracture. A reduction in the intensity of exercise, as long as it is effective in increasing the back extensor strength, may thus be beneficial for patients with osteoporosis. We hypothesized that back extensor strength would still increase with exercises in which resistance, number of repetitions, and frequency were lower than in our previous study. Our purpose in the present study was to determine the effects of reducing resistance, repetitions, and frequency of back-strengthening exercises on back extensor strength in healthy young women. METHODS 1299 Participants Healthy young female volunteers were recruited to participate through announcements to students enrolled in the College of Allied Medical Sciences at our university. Initial screening excluded women with any history of back pain or back injury in the past 12 months or any known health problems that would interfere with their participation. A total of 58 volunteers with a mean age of 20 years (range, 18 26y) participated in this study. All participants were given a comprehensive explanation of the study and its expected benefits and risks. All participants then signed an informed consent form approved by the institutional review board of our university. From the Departments of Orthopedic Surgery (Hongo, Itoi, Miyakoshi, Okada) and Rehabilitation (Shimada), Akita University School of Medicine, Akita, Japan; Department of Physical Medicine and Rehabilitation, Mayo Clinic, Rochester, MN (Sinaki). Presented to the 25th Annual Meeting of the American Society for Bone and Mineral Research, September 19 23, 2003, Minneapolis, MN. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to Michio Hongo, MD, Dept of Orthopedic Surgery, Akita University School of Medicine, Hondo, Akita , Japan, mhongo@doc.med.akita-u.ac.jp /05/ $30.00/0 doi: /j.apmr Measurement of Back Extensor Strength Back extensor strength was evaluated with an isokinetic dynamometer a at 0 (baseline), 4, 8, and 12 weeks. Measurements were performed in accordance with the procedures for measurement of back extensor strength described by Limburg et al. 12 Subjects were instructed to lie prone with hips and knees in the extended position and arms at the side of the body. Because no immobilizing straps were necessary, back extensor strength could be determined without contributions from the musculature of the lower extremities. The upper edge of the pad at the end of the arm was aligned with the superior borders of the scapulae across the midline. Strength was measured strictly isometrically, so that range of motion did not affect

2 1300 EFFECTS OF REDUCING RESISTANCE, REPETITIONS, AND FREQUENCY OF BACK EXERCISE, Hongo Table 1: Exercise Protocols Group Control STD WRD RRD FRD Weight of backpack (% of maximal isometric force back extensors could generate) Repetitions (repetitions/d) Frequency (exercise periods/wk) measurements. Back extensor strength was calculated by dividing isometric torque by arm length. Subjects were allowed 1 warm-up trial, followed by 3 successive maximal effort trials separated by 60-second rest periods. Maximal force from the 3 trials was selected and documented. Reproducibility was assessed in 10 healthy volunteers who underwent measurements on 2 separate days within 1 week. Intraexaminer reproducibility, as determined using the coefficient of variation, was 2.9% (M Hongo, unpublished data, 2001). All subjects underwent assessment by 1 examiner, who was blinded to group allocations. Evaluation of Level of Physical Activity Physical activity scores associated with housework, job, and sports and recreation were evaluated with a 7-point scale (range, 0 6). 13 This scale measured approximate range of energy cost and duration of activity, according to the tables provided by the American Heart Association. 14 Because high background levels of physical activity might affect the changes in back extensor strength, subjects with physical activity scores greater than 8 were excluded during the recruitment phase. Study Design Participants were randomly assigned to 1 of the following 5 groups: the control group (n 11), without exercise prescription; the standard (STD) group (n 11), with a standard protocol that has been shown to increase back extensor strength (weight lifted was 30% of the maximal isometric force back extensors could generate, 10 repetitions/d, 5d/wk) 9-11 ; the weight reduction (WRD) group (n 13), with the same protocol as the STD group except for reduced weight (15% of the maximal isometric force back extensors could generate); the repetition reduction (RRD) group (n 11), with the same protocol as the STD group except for fewer repetitions (5 repetitions/d); and the frequency reduction (FRD) group (n 12), with the same protocol as the STD group except for frequency of exercise (3d/wk) (table 1). Backpacks contained a weight equivalent to 30% (15% for the WRD group) of the maximal isometric force the back extensor could generate. Subjects in the exercise groups were instructed to lie in a prone position with a pillow under the abdominal region and the backpack on the back (fig 1). The weight of the upper edge of the backpack was aligned with the superior borders of the scapulae across the midline, to exert force from the backpack equal to 30% (15% for the WRD Fig 1. Back-strengthening exercise used by subjects in exercise groups. Backpacks contained weights. group) of maximal back extensor strength. The chest was then lifted off the ground toward the neutral position, avoiding extension of the spine to prevent back pain or injury. Each group maintained isometric muscular contractions for 5 seconds, then relaxed for 5 seconds. Each contraction was repeated 10 times (5 times for the RRD group) consecutively during each session. Exercises were done unsupervised at home at the convenience of participants. In each group, back extensor strength was measured every 4 weeks, and physical activity score was determined at baseline and 12 weeks. Weight inside the backpack was increased proportional to improvements in back extensor strength. All subjects were asked to keep diaries to record the amount of exercise performed, to maintain their regular diets, and to avoid initiation of any new athletic activities. Statistical Methods Differences in back extensor strength among the 5 groups at 12 weeks were assessed using 2-way repeated-measures analysis of variance (ANOVA). Differences in baseline characteristics and rate of change in back extensor strength among the 5 groups were assessed using 1-way factorial ANOVA. A P value of.05 or less was considered statistically significant. RESULTS Of the original 58 subjects, 51 completed the study. One control subject fractured her humerus while snowboarding and underwent open reduction and fixation. One subject in the FRD group fractured her ankle and was treated with casting. Two subjects in the STD group dropped out: 1 experienced low back pain (LBP) during the exercise period and the other reported back pain after performing the exercises. Another 3 subjects (1 from the RRD, WRD, and FRD groups) withdrew because they did not follow instructions or were not comfortable participating in the study. Subjects baseline characteristics are summarized in table 2. No significant differences were identified between the 5 groups with regard to age, height, weight, body mass index, or physical activity score. No significant differences in back extensor strength were identified between the groups at baseline or 4 weeks. At 8 weeks, back extensor strength was significantly greater in the STD group than in the WRD (P.025) or FRD (P.024) groups. At 12 weeks, back extensor strength was significantly greater in the RRD and STD groups than in the controls (P.029, P.01, respectively). Back extensor strength increased significantly in all groups except the controls by 12 weeks (table 3, fig 2). Back extensor strength at 12 weeks increased the most in the STD group (39%, P.001), followed by the FRD (25%, P.001), WRD (22%, P.001), RRD (20%, P.006), and control (5%, P.246) groups. Percentage change in back extensor strength was significantly greater in the STD group than in the other groups except the FRD group (table 3, fig 3).

3 EFFECTS OF REDUCING RESISTANCE, REPETITIONS, AND FREQUENCY OF BACK EXERCISE, Hongo 1301 Table 2: Baseline Characteristics of Subjects Group Control STD WRD RRD FRD P N (dropouts) 11 (1) 11 (2) 13 (1) 11 (1) 12 (2) NA Age (y) Physical activity score Height (cm) Weight (kg) BMI (kg/m 2 ) NOTE. Values are mean standard deviation (SD) or n. Abbreviations: BMI, body mass index; NA, not applicable. DISCUSSION Our study evaluated the effects of reducing weight, repetitions, and frequency of back-strengthening exercise on back extensor strength in healthy young women. We found that improvements in back extensor strength were obtained even after reducing the weight, number of repetitions, or frequency of exercise. Compared with the STD program, reducing the number of repetitions or frequency of exercise had less of an effect on back extensor strength than reducing weight. Techniques in Measuring and Strengthening Back Extensors Measurements of back extensor strength and back-strengthening exercises are more ideal if specific instruments are used to measure trunk strength in sitting positions with various spinal postures. 15 However, procedures for testing and strengthening back muscle in a prone position were essential for this study, because it was closely related to previous studies by Sinaki 9-11 and colleagues. Furthermore, the data obtained from this study will be applied to patients with osteopenia and osteoporosis in a follow-up study. We thus need to maintain methods for testing back extensor strength and performing back-strengthening exercises. The techniques used for measuring back extensor strength and procedures for back-strengthening exercises have been established as safe and reliable. 10,12 During measurement and exercise, a prone position allows back extensors to work without contributions from the musculature of the lower extremities. Effects of Reducing Frequency and Repetitions of Exercise Numerous studies have investigated frequency and repetitions of lumbar extension training. Graves et al 15 showed that a training frequency as low as 1 session/wk can provide effective training stimulus for the development of lumbar extension strength in rehabilitative treatment for LBP. However, the magnitude of daily exercise in that study was much greater than that in this study. Because the purpose of exercise differs between patients with osteoporosis and patients with LBP, data from studies examining treatment of LBP are not directly applicable to the management of osteoporosis, which predominantly occurs in elderly people. The most clinically appropriate frequency and number of repetitions for improving back extensor strength should thus be determined by the lesser amount of exercise. In this study, final back extensor strength was significantly greater in the RRD group than in the controls and did not differ significantly from that in the STD group. Percentage change of back extensor strength was significantly greater in the FRD group than in the controls and did not differ significantly from that in the STD group. These results indicate that reducing the frequency from 5 to 3d/wk may have less effect on improving back extensor strength than reducing repetitions from 10 to 5 repetitions/d or reducing weight from 30% to 15% of maximum back extensor strength in healthy young women. However, comparisons between these 3 reduced groups are difficult, because (1) repetitions and weight were reduced to 50% of the standard level, whereas frequency was reduced to 60% of the standard and (2) weight, repetitions, and frequency differ qualitatively. Our results suggest that reductions in weight, repetitions, or frequency result in decreases in the strength improvements obtained but are still better than no exercise regimen. Effects of Reducing Resistance There are few studies on the optimal intensity for achieving significant improvements in muscular strength among elderly populations. Vincent et al 16 described similar results after low-intensity (50% of 1 repetition maximum [1-RM]) and high-intensity (80% of 1-RM) lumbar exercises in 60- to 83- year-old subjects. Interestingly, the magnitude of increases for lumbar extensor strength with low-intensity lumbar exercise was greater than that with high-intensity lumbar exercise for certain postures. These results suggest that lower-intensity exercise may be useful for improving muscular strength in elderly people. Our study showed that exercise using a reduced weight was less effective for improving back extensor strength than was using a standard weight. However, reducing the weight may be advantageous for some patients, such as those with osteoporosis, in avoiding the potential risk of vertebral fractures. As long Table 3: Mean Back Extensor Strength Group Control STD WRD RRD FRD P Baseline (N) wk (N) wk (N) wk (N) % change in 12wk NOTE. Values are mean SD.

4 1302 EFFECTS OF REDUCING RESISTANCE, REPETITIONS, AND FREQUENCY OF BACK EXERCISE, Hongo as the exercise regimen is effective, we believe that the lighter the weight, the safer the exercise. In fact, 2 subjects in the STD group withdrew because of LBP and back pain. After they stopped exercising, their pain soon resolved. Pain in these cases was attributed to muscle, not bone. For these subjects, a weight of 30% of back extensor strength may have been too heavy to manage safely. Compliance With Back-Strengthening Exercise People participating in high-intensity exercise programs often reduce or stop training unless their motivation is maintained. Although the STD exercise protocol followed in our study used a lower weight than previously described, 16 2 participants quit the study because of pain after exercising. Compliance with an exercise regimen is critical for transposing a protocol to older populations. In addition to exercise intensity, convenience is also important. The exercises specified in this study can be performed at home in a few minutes with readily available equipment. Bone Mineral Density We did not evaluate bone mineral density (BMD) in our subjects. Our previous studies 9-11 have shown that BMD is unaffected by 2 years of back strengthening exercise in which the STD protocol was applied. The similar or lower intensity or frequency of back-strengthening exercise done in this study thus seems unlikely to have affected BMD. Application to Postmenopausal Populations Because the STD exercise might result in the development of back pain or injury, we investigated the effect of reducing the amount of exercise in young healthy premenopausal volunteers as a preliminary study. As a result, reducing weight, number of repetitions, or frequency to 50% to 60% of those used in the STD exercise regimen resulted in approximately 50% of the gains in back extensor strength achieved using the STD regimen. Elderly patients with osteoporosis and poor muscular condition reportedly respond better to exercise than do young healthy subjects. 17 Elderly populations may thus have greater opportunity for improvements to back extensor strength by doing less intense and less frequent exercise. Study Limitations Our study has several limitations. The lack of blinding to subject allocation and outcome testing may have influenced the Fig 2. Change in back extensor strength in the 5 study groups. At 8 weeks, back extensor strength was significantly greater in the STD group than in the WRD and FRD groups. At 12 weeks, back extensor strength was significantly greater in the RRD and STD groups than in the controls (CON). Values are mean SD. Fig 3. Percentage change in back extensor strength in the 5 study groups. Back extensor strength at 12 weeks was most increased in the STD group (39%), followed by the FRD (25%), WRD (22%), RRD (20%), and control (5%) groups. Percentage change in back extensor strength was significantly greater in the STD group than in any group other than the FRD group. Values are mean SD. results. Because the attention received from the study s staff varied among volunteers, subjects motivation may have varied with the amount of exercise. Previous studies 9,10 have found increases in back extensor strength in both exercise and control groups. Amounts of daily activity or exercise thus may change even in control subjects. Second, there was no supervision of compliance with exercises being done at home, although participants were instructed in the exercise method and asked to keep diaries in which they recorded exercise performance and sports activities. However, the back exercises recommended in this study offer the advantages of low cost, simplicity, and convenience. Another limitation concerns the small number of subjects involved, thus limiting the power of statistical analyses. However, this was a pilot study preceding a larger investigation of elderly subjects. Larger, randomized trials with older adults are required to determine more specific intensities and frequencies required to produce sufficient effects on back extensor strength. CONCLUSIONS Back extensor strength in the WRD, RRD, and FRD groups was significantly increased at 12 weeks compared with baseline. Reductions in weight, number of repetitions, or frequency to 50% to 60% of the standard regimen resulted in approximately 50% of the gains in back extensor strength compared with the STD group. Thus, people who are physically unable to perform the STD exercise program can still improve their strength through a less intense exercise program. Acknowledgments We thank Hitoshi Inaba, Shyunsuke Kudo, and Syoko Inomata for assistance in recruiting subjects. We also thank Mineyoshi Sato and Kazutoshi Hatakeyama for technical assistance. References 1. Itoi E, Sakurai M, Mizunashi K, Sato K, Kasama F. 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